Internal anatomy of pulp is complex. The first mandibular molars typically have two roots, one mesial with two root canals and another distal root, which contains one or two canals. A 20-year-old female patient reported with intermittent pain and incomplete root canal treatment in left lower back region since 1-week. Refined access cavity revealed initially two canals in mesial and two canals in the distal root. With operating microscope and cone beam computerized tomography, two additional canals (L-mesio-buccal and B-mesio-lingual) were identified in mesial root. One-year follow-up showed patient was asymptomatic and complete healing of periapical radiolucency.

A major cause of failure in endodontic treatment is the incomplete debridement of root canal system. [1] Pulp tissue remnants due to the inability to locate canals can affect and compromise the treatment outcome. [2] Thus, a better understanding of tooth morphology and anatomy is essential to attain this purpose. The mandibular first molar is considered to be the most common tooth to involve in the endodontic procedure because it is earliest permanent tooth to erupt. [3] Because of the greater number of endodontic treatments involving this tooth, the clinician may be confronted in many cases of mandibular first molars with variation in root (single root, [4] four roots, [5] taurodontism, [6] radix entomolaris, [7] Radix paramolaris [8] ) and internal anatomy (middle mesial, [9],[10],[11],[12],[13],[14] middle distal, [5],[9],[13],[14],[15],[16] and C-shape [17],[18] ). However, presence of four canals in the mesial root is extremely rare. [9],[10],[11],[12],[13],[14] This case report describes the endodontic management of mandibular first molar with four independent mesial canals (mesio-buccal [MB], L-MB, B-mesio-lingual [ML], ML) and two distal canals (disto-buccal [DB], disto-lingual [DL]) using operating microscope and cone beam computerized tomography (CBCT). [19]

Case Report

A 20-year-old female patient reported to Department of Conservative Dentistry and Endodontics, with an intermittent type of pain and incomplete root canal treatment in left lower back region since 1-week. Clinical examination revealed attempted root canal treatment in tooth #19 with no signs of pain or tenderness on percussion. The temporary restoration within the access cavity had been missing [Figure 1]a. Radiographic examination revealed periapical radiolucency in relation to the distal root. From clinical and radiographic examination, a diagnosis of chronic apical abscess was made on tooth #19.{Figure 1}

Under rubber dam isolation, access cavity was modified with endo access bur (Dentsply, Switzerland). Earlier two canals in mesial- and distal roots were identified. Working length was determined with the help of ISO 10 K-file. Under a dental operative microscope (7X, Seiler IQ, Chicago, USA) additional two more canals were identified in the mesial root (L-MB and B-ML) [Figure 1]b. A total six root canals were identified that is, MB, L-MB, B-ML, ML in the mesial root with (Type XIV) according to Sert and Bayirli's classification [20] and DB, DL in distal root (Type II) according to Vertucci classification. [21] An apex locator (Root ZX, J Morita Mfg. Corp., Japan) was used to verify the working length in all six identified root canals. An additional operative radiograph [Figure 1]c was then taken to confirm the independent presence of four canals in mesial root. Root canals were instrumented with ProTaper rotary Ni-Ti instruments (Dentsply, Maillefer) using crown down technique and alternate irrigation with 5.25% sodium hypochlorite and 17% ethylenediaminetetraacetic acid (EDTA). Cleaning and shaping was done till F 2 in mesial canals and F 3 in distal canals. After completion of the chemo-mechanical preparation, cavity was sealed with zinc oxide eugenol temporary cement (Dental products of India).

CBCT (Kodak 9000 3D, Carestream Dental LLC Vaughan, Canada) images were taken with the informed consent of the patient. Axial CBCT images, revealed independent four root canals in coronal and middle part of the mesial root and with only two canals in the apical axial image [Figure 1]d and [Figure 3] indicating a Type XIV canal pattern. Calcium hydroxide dressing placed and patient recalled after a week. After a week, intra-canal dressing was removed with alternate instrumentation and irrigation with 5.25% sodium hypochlorite. The canal was finally rinsed with saline and EDTA. The root canals were dried with paper points and obturated with sealer (Apexit, Ivoclar Vivadent) and respective Gutta-percha cones (Dentsply, Maillefer, Switzerland) using lateral condensation technique [Figure 2]a and [Figure 2]b. Temporary cement (Dental products of India) was placed and a postoperative radiograph was taken to assess the quality of obturation [Figure 2]c. One year follow-up showed patient is asymptomatic, and there is complete healing of periapical radiolucency [Figure 2]d.{Figure 2}{Figure 3}

DISCUSSION

The mandibular first molar is the first permanent tooth to develop at the age of 6 years. It is the most heavily restored teeth and also common to undergo root canal treatment in adult dentition. Normally, mandibular first and second molars have two roots, that is, mesial and distal root. The percentage of mandibular molars, with two canals in the mesial and one in the distal root is 65% and the presence of two canals in the distal root is 30%. Middle mesial or multiple canals in the mesial root of mandibular molars have been reported in the literature as having an incidence of 2.07-13.3% of the examined cases. [22],[23] The incidence of middle mesial canal (MMC) and middle distal canal in mandibular first one molar are 1-15% and 0.2-3%, respectively. [4],[20],[24] However, only six case reports have reported showing four canals in the mesial root of mandibular molars. [9],[10],[11],[12],[13],[25]

Figures have been named according to Valerian Albuquerque et al. Earlier Reeh described the nomenclature as MB1, MB2, ML1, ML2, DB, DL, but lacked the clarity based on their location. [9] However, the proposed naming system is an anatomically based nomenclature which takes into account the root-to-root-canal relationship in mandibular molars and its location. [26]

The existence of two MM canal is sometimes observed in horizontally angulated radiographs. Conventional radiograph exhibits two-dimensional views, whereas CBCT shows three-dimensional imaging with accuracy and precision and a promising tool for investigating the occurrences and morphology of root canal anatomy. Main disadvantage of CBCT compared to conventional radiograph is high radiation dose, but with proper precautions like lead sheath and thyroid collar its effect can be reduced. In this situation, CBCT provides additional information to detect extra canals. De Toubes et al., [27] in an in-vitro study demonstrated that CBCT was an accurate method of identifying accessory mesial canals in mandibular first molars. In the present case, CBCT was used to confirm the two MMCs with separate orifices but joined with other canals before exiting.

Nosrat et al. studied the frequency distribution of MMCs in mandibular molars and according to him, there were no significant differences in the incidence of MM canals based on sex, ethnicity, or molar type. There was no significant difference in the presence of a second distal canal between the teeth with a MM canal and those without MM canal which is evident in [Table 1] mentioned above. Among 15 MM canals, 7 showed confluent anatomy, 3 independent anatomy, and 5 showed fin anatomy. Overall, 4% (2/50) of mandibular first molars had a second distal (DL) root and 8% (2/25) of mandibular second molars had C-shaped anatomy. [28] {Table 1}

Reuben J, Velmurugan N, Kandaswamy D. The evaluation of root canal morphology of the mandibular first molar in an Indian population using spiral computed tomography scan: An in vitro study. J Endod 2008;34:212-5.